Ausra, a solar thermal specialist from Australia, on Thursday said it will try to build solar power plants in the U.S. over the next seven years that collectively will generate a gigawatt worth of power. Three hundred megawatts worth of that capacity is already committed to FPL Group, a utility concentrated in Florida, according to Ausra.

Another likely customer is Pacific Gas & Electric. The California utility has committed to signing contracts for a gigawatt worth of solar thermal power over the next five years. PG&E is talking to a number of solar thermal companies about this, including Ausra.

These plants, along with the other solar power plants in the planning stages, will greatly expand the footprint for solar thermal power. Solar thermal plants concentrate sunlight onto mirrors to collect heat, and then use the heat to create steam or gas from an enclosed liquid. The pressure from the gas then turns a turbine to create electricity.

The biggest solar plant in the world right now, in California's Mojave desert, can generate around 354 megawatts. It was built 22 years ago. Acciona Solar Power earlier this year inaugurated the first solar thermal plant in over a decade anywhere in the world. It sits outside of Las Vegas.

Large plants--like the 300 megawatt plant Ausra will build for FPL--could also help bring down the cost. Right now, solar thermal power costs more than regular power from gas or coal-burning plants. But scientists, venture capitalists and analysts have said that solar thermal plants can be comparable in cost if built large enough. The rough estimate is that a 500 megawatt solar plant, or a couple of 300 megawatt solar plants built close to each other, could be comparable with traditional electricity. The cost projections, however, all vary according to environmental conditions, proximity of large cities to the power plant and construction costs.

Utility company Southern California Edison is erecting a 500-megawatt plant scheduled to open in 2009.

Large conventional power plants can often put out around 500 megawatts.

Besides building large power plants, Ausra, which recently raised $40 million, says it can cut the costs in other ways. Unlike a lot of solar thermal companies, Ausra doesn't used curved mirrors to collect sun or oil to fill its heat collectors. Instead, it uses cheaper flat mirrors and water.

Earlier this month, Ausra CEO Peter Le Lievre told an audience at the Going Green conference that a solar thermal plant in the desert measuring 92 miles by 92 miles built with his company's technology could provide all of the electricity in the country.

"We are more than two times more efficient when it comes to land," he said. "We are at 10 cents a kilowatt hour today," he said. With mass manufacturing, we will fall below gas (natural gas plants) and beat coal."

The company is currently trying to get a permit to build a 175-megawatt plant in California that would take up a square mile.

Of course, this could all change. Utilities are buying solar thermal because of state mandates. Ausra also faces several competitors.